Abstract
Since early 2021, peculiar Volcano-Tectonic (VT) seismic sequences with very short inter-event times have become increasingly frequent and evident in the Campi Flegrei caldera (Italy), which has been experiencing a long-term unrest since 2005. During the same period the ground deformation (uplift), seismicity and gas emission that characterize the current unrest showed an acceleration. Within this type of seismic sequence, we identify burst-like swarms, characterized by inter-event times so short that they are often not easily recognizable. Here we show that these sequences are located in an area encompassing the main hydrothermal field and a zone affected by a geodetic anomaly (a region that uplifts less rapidly than the surroundings), which became evident in 2021. This type of seismicity has been associated with phreatic explosions and critical phases of unrest in other volcanoes and currently characterizes the state of activity of Campi Flegrei caldera.